For those that don't know, PLEX is in an item that enters the game economy via a real world purchase (£16.99 at time of writing). The item can then be sold in game for ~600 Million ISK (the in game currency), redeemed for subscription time or used to activate multiple character training. This allows players to pay for their subscription with ISK and allows players with limited play time but more disposable income to get ISK to fund their activities. For example, I know that many players invest in an ISK per month on top of their subscription to fund their ships in PvP and minimise their time spent farming. Although ISK cannot be legally transferred into real money, due to PLEX having both an ISK value and real world value, it allows a pseudo-real world value to be applied to various items in the game and provide nice headlines for the gaming media such as the "~$300,000 destroyed in the battle of B-R" equating to over 10 trillion ISK.
In the first paragraph highlighted a few positives. Firstly, this offers an alternative to players who don't necessarily have the disposable income to pay the subscription fees. Secondly, it allows players with limited playtime but extra disposable income to get engaged in activities that cost ISK such as PvP. This is good because more players engaging in PvP, or other ISK losing activities, means more content. More content in a sandbox world is always a good thing. Thirdly it is also a great marketing tool. The battle of B-R is an example where media can put real world values on the destruction in game to draw the attention of players who wouldn't otherwise take notice of the EVE universe. This leads to spikes in player population which is always good for the health of the game. However, I also feel there are a number of negatives associated with PLEX.
I think it often causes a problem in expectation management. When I hear EVE players trying to get friends or other gamers interested in playing the subscription fee almost always comes up. When it does, it is almost always followed with "but if you earn enough currency in game you can pay for subscription that way". While true, and a good way to draw them into taking the free trial, I think it sets a dangerous precedent. It can cause new players to become entirely focused on making enough ISK to buy a PLEX rather than just enjoying the game during that trial. Very few new players make enough ISK in their free trial be able to PLEX an account. Making ISK can become an obsession for a lot of players, counting the hours to that next PLEX. I know that when I started out I spent a lot of time wondering about the ISK/Hour for each of my activities, rather than if I really enjoyed some of them. Thankfully Brave Newbies cured me of that illness and now I only engage in ISK making activities that I actually enjoy, regardless of ISK/Hour.
The other point I want to touch on is the altered perception of the game that it can give outsiders. "$300,000 destroyed in EVE online". It is quite a head turning statement. I believe the majority understand that nobody really spent $300,000 to blow up spaceships in a videogame. Sure, some of the ISK used to obtain ships lost in the battle will have come from PLEX sales, though I would expect that to be a small fraction of the total. My concern is that there will be a subset of potential players turned away by this headline because they don't take the time to understand it fully. There will be players who immediately conjure up a cash shop in their minds, common in other games, immediately connecting that money with the direct purchase of ships. The dreaded "Pay to Win" will be a concern of others, possibly putting them off the game*. There will also be non gamers who see the headlines but don't actually read deeper into the article, negatively affecting their perception of EVE players and the Universe that they inhabit.
Overall I do think PLEX is a good thing in EVE online. It has other benefits not described earlier, such as the pressure it places on RMT sellers. I think the amount of players it brings to the game outweighs those that it turns off, evidenced by the spikes in trial accounts and subscriptions following the major battles that make it into the media. Though the altered perception it can give to others is an interesting thought. The ability for less financially prosperous players to get in on the action, along with the flip side of that particular coin being able to generate content, can only be a boon to the population of the game. Though, I do often wonder the problems that it can lead to with ISK obsession and how it affects the motivations of new players entering the game. It makes me wonder what the EVE landscape would be like if PLEX didn't exist. Just some food for thought.
* The "Pay to Win" idea is a contentious point regarding PLEX and one that I will at some point dedicate a post towards